This invention concerns conveyors and more particularly gravity conveyors in which load carrying carriers roll down an inclined lower track from a loading end to an unloading end of the track, the carriers returned on a reversely elevated inclined return track back to the loading end.
The present inventor has previously patented a gravity conveyor in which a power mechanism pushes each carrier around a partially circular end track which curves upwardly from the unload end of the lower track to the upper end of the return track. The upper track is inclined down towards the loading end of the conveyor to be converging with the lower track at the loading end so that the carriers by gravity roll back to the loading end. See U.S. Pat. No. 5,590,756 issued on Jan. 7, 1997.
In another known gravity conveyor, the lower and upper tracks are parallel to each other, and both are inclined downwardly from the loading end to the unloading end of the conveyor. Instead of powering the carrier movement to the upper track and using a downward inclination of the upper track to return the carriers, the carriers are all linked together into a train by a roller guided chain routed within the tracks.
By linking the carriers together, an equilibrium condition is reached when all the carriers on the lower track are loaded, the weight of the loaded carriers on the lower track pulling through the chain on a lead loaded carrier to cause it to partially ascend up the curved return track section at the unload end. The weight of the load on the lead carrier balances the component of the weight of the train of loaded carriers on the lower track directed down the lower tracks. When the load is removed from the lead carrier, this equilibrium is upset and the other load carriers are advanced sufficient to cause a new lead carrier to ascend the track end and reestablish the equilibrium position down the track when a load is placed on the last carrier at the loading end.
Thus, the carriers are successively pulled incrementally around the unloading end tracks in increments and also pulled up along the inclined upper track back to the loading end in the same fashion, as load items are removed at the unload end and added at the load end. However, this conveyor, using a heavy roller guided chain in the track, generates considerable friction. This friction can lead to sluggish performance of the conveyor and prevent use of the conveyor with loads that are too light to overcome the friction.
The cost of the conveyor is also increased by the cost of the roller guided chain.
Another drawback of this previously known conveyor is that the end tracks are constructed of formed extrusion sections of the same configuration as that of the upper and lower tracks, requiring a large radius of the end tracks since the tracks cannot be formed into a tight radius. This increases the bulk of the conveyor.
It is an object of the present invention to provide a linked carrier gravity conveyor of the type described in which chain friction caused by dragging of the chain in the trackway is eliminated.
Another object of the present invention is to provide a linked carrier gravity conveyor of the type described which is simpler and less costly than previous such conveyors.